In a motor vehicle, it is known practice to use presence detection devices for detecting the presence of a hand or of a foot of a user of the vehicle and thus to allow all or some of the doors of the vehicle, for example the passenger doors or the trunk, to be locked or unlocked. By way of example, the detection of the presence of a hand of a user on or in front of a door handle in conjunction with the recognition of an identifier of a “hands-free” access device carried by this user allows these doors to be locked and unlocked.
To achieve this, when the user approaches the vehicle, communication is established over a wireless communication link between the access device, for example an electronic badge or a cell phone, and the detection device in order to authenticate said access device by means of its identifier.
To this end, the detection device includes an antenna allowing the identifier transmitted by the access device to be received. The detection device is connected to the vehicle's electronic computer (ECU: abbreviation for “electronic control unit”) to which it transmits the identifier.
According to the prior art, the access device is generally an electronic badge. The signal received by the antenna of the detection device, comprising the identifier of the access device, is transmitted via RF (radiofrequency) or LF (low-frequency) waves.
Nowadays, however, it is increasingly common to use a cell phone to perform authentication functions, which makes it possible to avoid using a dedicated electronic badge and thus to limit the number of devices. Since the majority of cell phones do not have RF or LF communication means, it is known practice to use the near-field communication, or NFC, module, with which the majority of modern phones are provided, to transmit the identifier of the device in the case of a function of unlocking a vehicle.
The access device coming into proximity of (less than 10 cm away from) the detection device and the identifier received by the computer being recognized, in conjunction with the hand of the user being detected, allows the door to be locked or unlocked.
To detect the presence of the hand of the user and to allow the doors of the vehicle to be unlocked, such a detection device comprises, in a known manner, a capacitive sensor. Generally, a capacitive sensor is dedicated to one detection zone and, according to the prior art, there is one capacitive sensor for the unlocking zone and one capacitive sensor for the locking zone, the two zones being distinct.
According to one example of capacitive measurement, such a capacitive sensor comprises a first capacitor that is charged and discharged periodically from/into a second capacitor. When the first capacitor discharges into the second capacitor, the charges are balanced between the two capacitors.
When a hand is present on the handle or close to the handle, for example less than 10 mm away, the level of charge of the first capacitor increases. This results in a larger discharge of the first capacitor into the second capacitor, and therefore a higher level of balancing in the presence than in the absence of a hand on the handle. Such a sensor thus makes it possible to detect the intention of the user to unlock the doors of the vehicle.
However, using capacitive sensors has a number of drawbacks.
Specifically, the detection of the approach of a user by capacitive sensors is not robust and generates false detections.
In particular, in some environmental conditions, when the ambient air is humid or when there is salt on the roads, which is spattered onto the metal bodywork of the vehicle, capacitive coupling is created between the detection zones and the metal parts of the vehicle, thereby preventing any detection of the presence of a user by the capacitive sensors.
In addition, raindrops or snowflakes on the door handle increase the capacitance measured by the capacitive sensors, thus triggering false detections.
Lastly, detection by capacitive sensors is incompatible with handles coated with metallic paints or comprising chromed surfaces, the presence of metal in the handle creating a coupling with the detection zones and inhibiting the detection of the presence of a user.
While, for some vehicles, false detections are not desirable, for other vehicles, false detections are not tolerable.
This is the case for vehicles fitted with deployable handles, i.e. the case of handles for which the detection of the presence of the user controls the movement of a motorized handle which, when at rest, is completely incorporated within the door and, when activated, is deployed out of the door. For this type of handle, the unwanted deployment or retraction of the handle due to a false detection by the capacitive sensors risks hitting or squeezing the hand of the user.
This is also the case for vehicles provided with electrically assisted opening, for which the detection of unlocking is accompanied not only by the door being unlocked but also by it opening. In this case, false detections result in unwanted openings of the door.
Lastly, false detections are not tolerable for vehicles provided with the “safe lock” security function, for which the detection of locking controls not only the locking of the vehicle from the outside but also the locking of the vehicle from the inside (anti-theft device). In this case, false detections may lead to the user being shut inside the vehicle.
To overcome these drawbacks, it is known practice in the prior art to replace at least one of the capacitive sensors, for example the capacitive sensor dedicated to locking the vehicle, with a pressure detection sensor, for example an inductive sensor comprising a metal target which moves toward a coil of the sensor when the user presses on the locking or unlocking zone. The variation in inductance of the coil of the inductive sensor, due to the target approaching the coil, allows the detection of the intention of the user with regards to locking or unlocking to be validated.
However, incorporating a device for communication by NFC and an inductive pressure detection sensor within one and the same vehicle door handle has several drawbacks. The first drawback lies in the positioning of the two devices: the coil of the inductive sensor and the coil of the NFC sensor must not be located facing one another since they interfere with one another. Specifically, any metal part located close to the NFC antenna, for example the target or the coil of the inductive sensor, absorbs a portion of the electromagnetic field emitted by said NFC antenna and affects detection and communication with the portable device. Stacking the two devices in the handle is therefore not conceivable, so they must be located beside one another. However, since the space in handles is increasingly restricted (with a view to the esthetics of the handle), mechanically incorporating the components side by side is not always possible due to a lack of space.